Engines are usually designed with the ability to deliver a peak output, although most engine operation is performed well below this peak value. As such, it can be beneficial to operate with some cylinders inducting air without fuel injection, and other combusting air and injected fuel, as described in U.S. Pat. No. 6,568,177. By disabling some of the cylinders on the engine when desired output, such as torque, is relatively low, the engine can be operated at a higher manifold pressure to supply the needed airflow to the operating cylinders, thus reducing engine pumping losses and making the engine more efficient. In one example, the system can also use lean combustion and a NOx trap to avoid NOx emissions, and further improver efficiency. In a camless engine with electromechanical or electrohydraulic valve actuation (EVA), disabling some of the cylinders at idle may make the control of valve timing easier because the intake valve can be open longer on the operating cylinders. As such, there are various ways in which cylinder deactivation can be used to advantage during idle conditions, as well as other conditions.
However, the inventors here have recognized that, in some cases, repeated misfiring of one or more cylinders that is carrying out combustion, can lead to ineffective decisions as to whether and how cylinder deactivation is carried out.
The above disadvantages can be overcome by a method for operating an engine having at least a first and second cylinder, the method comprising:
operating in a first mode with said first cylinder combusting inducted air and injected fuel and said second cylinder inducting air and substantially no injected fuel;
operating in a second mode with said second cylinder combusting inducted air and injected fuel and said first cylinder inducting air and substantially no injected fuel;
operating in a third mode with both said first and said second cylinder combusting inducted air and injected fuel;
monitoring the first and second cylinder for an engine misfire condition; and
disabling said first mode if an engine misfire condition is detected in said second cylinder and disabling said second mode if an engine misfire condition is detected in said first cylinder.
In this way, it is possible to modify the selection and/or enablement of cylinder deactivation to account for potential engine misfire conditions.